With decreasing availability of fossil carbon resources, there is bound to be an increasing demand for alternative resources for chemical energy carriers and functional molecules. Biomass feedstocks present an enormous potential in this respect, as they are renewable and can be CO2 neutral. In contrast to crude oil, however, biomass and biomass-derived materials typically contain large concentrations of oxygenates. In most cases, the oxygen atoms are removed as water during deoxygenation processing, and, in some cases such as pyrolysis oil, the feed already contains large amounts of water.
Water is known to have a deactivating effect on many catalytic systems used in refinery-type processes. Catalysts containing alumina are known to be very sensitive to water, even at very low concentrations (in the parts per million range). Several prior art references describing catalyst compositions effective for deoxygenation also note the necessity for maintaining low oxygenate concentrations in the feedstocks.
For instance, the article by J. Hancsok et al. (Microporous and Mesoporous Materials, 101 (2007), 148-152) describes a metal/zeolite catalyst used for isomerizing oxygenate-containing feedstocks. The catalyst is bound with alumina, and it is noted that oxygenate contents of just over 1% in the feedstock cause a 50% acidity loss, indicating a reduced conversion activity. Additionally, the article by O. V. Kikhtyanin et al. (Fuel, 89 (2010), 3085-3092) describes a metal/SAPO catalyst, also bound with alumina, which is used for hydroconversion of sunflower oil. It was noted that fast deactivation was observed in tandem with high oxygenate concentrations (relative to non-oxygenated hydrocarbon concentrations), although the goal of the study was to find processing conditions that mitigated such issues.
Indeed, catalysts containing alumina can be among the most effective catalysts for many necessary processes, such as heteroatom removal (e.g., deoxygenation) and isomerization. Water-induced deactivation of such catalysts can occur via numerous mechanisms (e.g., sintering, titration of acid sites, competitive adsorption, zeolite support dealumination, and reduction of mechanical stability, inter alia), and such deactivation should be an increasingly important issue, due to the increasing demand for biofuels and other biomass-derived products.